1. Field of the Invention
The invention relates to downhole inspection and treatment systems and, more particularly, to a system for enabling the concurrent injection of fluid into a borehole and the performance of axillary downhole activities such as inspection and/or measurement. The invention may be practiced during maintenance and servicing of oil, gas, geothermal and injection wells.
2. History of the Prior Art
In the drilling and production of oil and gas wells, it is often necessary to obtain at the surface information concerning conditions within the borehole. For example, tools and other objects may become lodged in the borehole during the drilling of a well. Such objects must be retrieved before drilling can continue. When the removal of foreign objects from a borehole is undertaken, known as "fishing", it is highly desirable to know the size, position, and shape of the obstructing object in order to select the proper fishing tool to grasp the object and remove it from the borehole. Such information is very difficult to obtain because of the hostile downhole environment within a borehole filled with opaque drilling fluid.
In the operation and/or periodic maintenance of producing injection wells, it is also frequently necessary to obtain information about the construction and/or operating condition of production equipment located downhole. For example, detection of the onset of corrosion damage to well tubing or casing within a borehole enables the application of anti-corrosive treatments to the well. Early treatment of corrosive well conditions prevents the highly expensive and dangerous replacement of corrosion damaged well production components. Other maintenance operations in a production well environment, such as replacement of various flow control valves or the inspection of the location and condition of casing perforations, make it highly desirable for an operator located at the surface to obtain accurate, realtime information about downhole conditions. The presence of production fluids in the well renders accurate inspection very difficult.
Various techniques have been proposed for obtaining at the surface information about the conditions within a borehole. One approach has been to lower an inspection device, such as an optical or acoustical sensor positioned on the end of section of reeled tubing, into the borehole and produce a slug or "bubble" or optically transparent and/or acoustically homogenous fluid within the borehole to enable the accurate inspection by the inspection sensor attached to the lower end of the tubing. Such a system is shown in U.S. Pat. No. 4,938,060 to Sizer et al and assigned to the assignee of the present invention. This system is a major improvement over prior art inspection systems. However, in the application of certain techniques taught in the Sizer et al patent it is desirable to provide other types of downhole sensing devices within a region of an injected fluid to enhance the accuracy with which such sensor measurements are taken. For example, it may be desirable to inject a pill or slug of corrosion inhibiting material into a borehole having an extremely caustic environment in order to simply enable the measurement of certain parameters within that borehole without the destruction of the measuring instruments or sensors.
In addition, in the case of optical inspection sensors of the type shown in the Sizer et al patent, it is also desirable to provide a means for simultaneously cooling the downhole sensor equipment as well as injecting the optically transparent and/or acoustically homogenous fluid within the borehole which enhances the observation and inspection functions performed by the equipment.
It would be improvement in downhole inspection systems if an optically clear and/or acoustically homogenous fluid could be directly injected into the borehole in a zone where a multiplicity of different inspection devices could be positioned for use. In addition, it would be desirable to provide such an injection system which also simultaneously provides a cooling function within the sensor equipment and, ejects the fluid at a location with respect to the sensor which enhances the inspection activity.